More particularly, the original object of the invention was to design a mechanism further capable of having two distinct operating modes, one corresponding to all of the fluid working chambers being fed periodically with fluid under pressure, and the other corresponding to fluid being fed only to those working chambers that belong to a first group of fluid working chambers, with the other fluid working chambers no longer being fed with fluid under pressure in other words the mechanism was to have at least two distinct operating cylinder capacities. In a known technique for providing such a mechanism, it is necessary to provide at least three, and sometimes four distinct main enclosures, and it is necessary to provide balancing between the pressure forces that tend to separate the distribution face of the internal fluid distributor from the cylinder block communication face, enclosure by enclosure. These enclosures, of which there are at least three, follow one another axially at the periphery of the internal fluid distributor, being separated from one another by sealing gaskets, such that the axial length of the internal fluid distributor is relatively long, and it is desirable for said length to be reduced. One solution that has been proposed consists in replacing at least one and sometimes two main enclosures by one or two secondary enclosures that are no longer placed at the periphery, but inside the internal fluid distributor, which for a mechanism including four enclosures, corresponds to an axial extent that corresponds to an axial succession of only two main enclosures.
In that novel scheme, although the pressure forces corresponding to the fluid contained in the distribution ducts communicating with said two main enclosures can be balanced, in a manner known per se, by a judicious selection of shapes for the walls delimiting said main enclosures, it has been observed that the pressure forces relating to the fluid contained in the distribution ducts communicating with the internal secondary closure(s) cannot be balanced by selecting the shapes of the walls delimiting said internal secondary enclosure(s) which are, in fact, constituted by at least some of the distribution ducts themselves.
A first object of the invention is therefore to solve this problem of balancing the pressure forces of the fluid contained in the internal secondary enclosure(s) of such a mechanism having two distinct operating cylinder capacities, however, the object of the invention is wider than that and is not limited merely to implementing such mechanisms having a plurality of operating cylinder capacities. The invention is also advantageous for a mechanism having only one operating cylinder capacity. Thus, although in the first case of a mechanism having two operating cylindrical capacities, the actual length of the internal distributor can be considerably reduced, thereby making it possible to improve the mobility of said internal distributor which is less constrained by the various radial bearing surfaces delimiting the main enclosures, and thus making it possible, essentially, to improve contact sealing between the distribution face and the communication face of said mechanism, it has also been observed that it is possible to provide a mechanism having only one operating cylinder capacity even when the cam is secured to a structure identical to that of the mechanism having at least two operating cylinder capacities. This structure secured to the cam is a large and expensive part of the mechanism, and clearly it is advantageous for it to be common to the mechanisms of a manufacturing range including both mechanisms having a plurality of operating cylinder capacities and mechanisms having single operating cylinder capacities. By using a single structure secured to the cam, pressure forces are indeed balanced both in mechanisms having a plurality of operating cylinder capacities and in mechanisms having single operating cylinder capacities.
The ambit of the invention is therefore not limited to mechanisms having two operating cylinder capacities.